. Microsporidiosis is becoming recognized more frequently as a cause of human disease, especially in the immunocompromised host. Thus, several microsporidian organisms have been implicated in disease in HIV patients: Encephalitozoon sp. have caused keratoconjuctivitis and fatal hepatitis, Nosema sp. have caused disseminated disease and corneal ulceration, Pleistophora sp. have caused myositis and Enterocytozoon bienseusi (found in enterocytes) has been implicated in diarrhea. Diagnosis of these infections is problematic at best, requiring invasive procedures and electron microscopy for visualization of the parasites. Recently, the investigators claim to have been able to demonstrate these organisms by Giemsa staining. There exists a need for noninvasive diagnostic tests for these organisms to allow epidemiologic studies and in vitro and in vivo models for drug screening. The applicants further claim to have identified several common antigens among the various microsporidian parasites and propose to utilize these to develop antigen diagnostic tests through the production of polyclonal and monoclonal antibodies. In addition, genus specific antigens will be sought to allow further definition of isolated organisms. The investigators also state that they have developed a PCR reaction capable of detecting microsporidian organisms and propose to further extend this procedure looking for common as well as specific primers for these organisms by examining CDNA libraries and amplified rRNA sequences.